feat: support option for setting client-id

Author: aakashanandg

google-cloud-spanner/clirr-ignored-differences.xml

@@ -964,11 +964,4 @@
     <className>com/google/cloud/spanner/DatabaseClient</className>
     <method>com.google.cloud.spanner.Statement$StatementFactory getStatementFactory()</method>
   </difference>
-
-  <difference>
-    <differenceType>7012</differenceType>
-    <className>com/google/cloud/spanner/Spanner</className>
-    <method>com.google.cloud.spanner.DatabaseClient getDatabaseClient(com.google.cloud.spanner.DatabaseId, java.lang.String)</method>
-    <justification>Added as default method for JDBC client ID support. Default implementation throws UnsupportedOperationException to maintain binary compatibility for existing implementers.</justification>
-  </difference>
 </differences>

google-cloud-spanner/src/main/java/com/google/cloud/spanner/ExtendedSpanner.java

@@ -0,0 +1,28 @@
+package com.google.cloud.spanner;
+
+public interface ExtendedSpanner extends Spanner {
+  /**
+   * Returns a {@code DatabaseClient} for the given database and given client id. It uses a pool of
+   * sessions to talk to the database.
+   * <!--SNIPPET get_db_client-->
+   *
+   * <pre>{@code
+   * SpannerOptions options = SpannerOptions.newBuilder().build();
+   * Spanner spanner = options.getService();
+   * final String project = "test-project";
+   * final String instance = "test-instance";
+   * final String database = "example-db";
+   * final String client_id = "client_id"
+   * DatabaseId db =
+   *     DatabaseId.of(project, instance, database);
+   *
+   * DatabaseClient dbClient = spanner.getDatabaseClient(db, client_id);
+   * }</pre>
+   *
+   * <!--SNIPPET get_db_client-->
+   */
+  default DatabaseClient getDatabaseClient(DatabaseId db, String clientId) {
+    throw new UnsupportedOperationException(
+        "getDatabaseClient with clientId is not supported by this default implementation.");
+  }
+}

google-cloud-spanner/src/main/java/com/google/cloud/spanner/Spanner.java

@@ -125,31 +125,6 @@ public interface Spanner extends Service<SpannerOptions>, AutoCloseable {
    */
   DatabaseClient getDatabaseClient(DatabaseId db);
 
-  /**
-   * Returns a {@code DatabaseClient} for the given database and given client id. It uses a pool of
-   * sessions to talk to the database.
-   * <!--SNIPPET get_db_client-->
-   *
-   * <pre>{@code
-   * SpannerOptions options = SpannerOptions.newBuilder().build();
-   * Spanner spanner = options.getService();
-   * final String project = "test-project";
-   * final String instance = "test-instance";
-   * final String database = "example-db";
-   * final String client_id = "client_id"
-   * DatabaseId db =
-   *     DatabaseId.of(project, instance, database);
-   *
-   * DatabaseClient dbClient = spanner.getDatabaseClient(db, client_id);
-   * }</pre>
-   *
-   * <!--SNIPPET get_db_client-->
-   */
-  default DatabaseClient getDatabaseClient(DatabaseId db, String clientId) {
-    throw new UnsupportedOperationException(
-        "getDatabaseClient with clientId is not supported by this default implementation.");
-  }
-
   /**
    * Returns a {@code BatchClient} to do batch operations on Cloud Spanner databases. Batch client
    * is useful when one wants to read/query a large amount of data from Cloud Spanner across

google-cloud-spanner/src/main/java/com/google/cloud/spanner/SpannerImpl.java

@@ -59,7 +59,7 @@
 import javax.annotation.concurrent.GuardedBy;
 
 /** Default implementation of the Cloud Spanner interface. */
-class SpannerImpl extends BaseService<SpannerOptions> implements Spanner {
+class SpannerImpl extends BaseService<SpannerOptions> implements ExtendedSpanner {
   private static final Logger logger = Logger.getLogger(SpannerImpl.class.getName());
   final TraceWrapper tracer =
       new TraceWrapper(

google-cloud-spanner/src/main/java/com/google/cloud/spanner/connection/ConnectionImpl.java

@@ -58,6 +58,7 @@
 import com.google.cloud.spanner.DatabaseId;
 import com.google.cloud.spanner.Dialect;
 import com.google.cloud.spanner.ErrorCode;
+import com.google.cloud.spanner.ExtendedSpanner;
 import com.google.cloud.spanner.Mutation;
 import com.google.cloud.spanner.Options;
 import com.google.cloud.spanner.Options.QueryOption;
@@ -328,8 +329,11 @@ static UnitOfWorkType of(TransactionMode transactionMode) {
     final DatabaseId databaseId = options.getDatabaseId();
     try {
       Optional<String> clientIdOpt = extractClientIdOptional(options);
-      if (clientIdOpt.isPresent()) {
-        tempDbClient = spanner.getDatabaseClient(databaseId, clientIdOpt.get());
+      if (clientIdOpt.isPresent() && !clientIdOpt.get().isEmpty()) {
+        if (this.spanner instanceof ExtendedSpanner) {
+          ExtendedSpanner extendedSpanner = (ExtendedSpanner) this.spanner;
+          tempDbClient = extendedSpanner.getDatabaseClient(databaseId, clientIdOpt.get());
+        }
       }
     } catch (Exception e) {
       System.err.println(